1. Field of Use
This invention relates to a seat suspension for resiliently mounting a seat on a support frame of a vehicle and more specifically to an improved seat suspension system ergonomically designed to reduce repetitive motion induced injury.
2. Description of the Prior Art
Most off-highway vehicles such as tractors and the like have an unsprung chassis. It is conventional practice to mount a seat for such vehicles on some type of resilient suspension means to permit the seat to have a range of floating up and down motion to minimize jolting of the vehicle operator.
In normal operation of the vehicle this floating will be a repetitive up and down motion. Seat suspensions have also included a dampening means designed to soften such repetitive motions, but dampening means do not prevent such motions. Medical experts have learned that seemingly innocuous repetitive motions can result in strains that take an excruciating toll on the human body in the form of cumulative trauma. Such innocuous movements occurring repeatedly may lead to leg, back, shoulder and neck pains or even chronic injury.
Many of the prior art resilient seat suspensions use upper and lower spaced parallel links to interconnect a base part of the seat suspension with a vertically movable seat support to maintain the actual seating surface at a preselected uniformly constant attitude relative to horizontal throughout the range of vertical float. Typical examples of upper and lower parallel link seat suspensions for maintaining the seat surface at one attitude are shown in U.S. Pat. No. 3,335,996 issued Aug. 15, 1967 to G. O. Hall et al; U.S. Pat. No. 3,493,211 issued Feb. 3, 1970 to C. J. Barecki et al; U.S. Pat. No. 4,222,555 issued Sep. 16, 1980 to S. H. Eimen; and U.S. Pat. No. 3,917,209 issued Nov. 4, 1974 to A. J. Adams. The floating action is usually provided by a vertically orientated spring means and the last-mentioned patent to Adams, for example, discloses a vertically orientated compression spring between the upper link and the base part to resiliently support the seat. The previously mentioned U.S. Pat. No. 3,335,996 uses an air spring between the base part and the movable seat support to achieve the same purpose. All of these seat suspensions maintain the seating surface at a uniformly constant attitude relative to horizontal. The use of a vertically orientated spring increases the overall height of the suspension and makes installation more difficult on small vehicles such as lawn and garden tractors where very limited vertical height is available for the seat assembly.
It is also known to provide a seat suspension with upper and lower links that are nonparallel and of unequal length as shown in U.S. Pat. No. 3,572,828 issued Mar. 30, 1967 to Wilhein Lehner; and U.S. Pat. No. 4,083,599 issued Apr. 11, 1978 to E. J. Gaffney. In the nonparallel linkage of U.S. Pat. No. 3,572,828 a vertical extension spring is connected to a link that has a floating pivot connection so while the seat will float vertically the preselected constant attitude of the seating surface does not change. In U.S. Pat. No. 4,083,599 the seat does not float and the upper and lower links only cause the seat to tilt and change the attitude of the seating surface when a power ram is extended or retracted to assist an occupant in leaving or sitting down on the chair.
In a resiliently suspended seat, the vertical distance between the occupant's knees and feet remains constant regardless of the vertical position of the seat as it floats. With floating suspension systems as above discussed, the attitude of the seating surface relative to horizontal remains constant as the seating surface moves up or down, and therefore the seating surface will not fully support the occupant's thigh between the hip and knee throughout the full range of seat float.
The prior art seat suspensions also normally make provision for a front to rear position adjustment of the seat assembly as a unit by releasably mounting a base part of the seat suspension on tracks. The seat suspension normally includes a latch lever that is selectably moved to release the seat base to slide on the tracks. Heretofore, latch levers have used a mounting assembly that is unduly complex requiring the manufacture of a plurality of parts which adds to the expense. Further, the final assembly of the latch lever and its mounting assembly on the base part of the seat suspension has been labor intensive and expensive.